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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Experimental and Analytical Studies on Damage Detection and Failure Analysis of Transmission Towers and Tower like Structures

Balagopal, R January 2016 (has links) (PDF)
The transmission line (TL) tower is an important component in electrical network system. These towers consist of members (angle sections) and connections (bolted connections) plus foundation, which act together to resist externally applied loads. The latticed towers are used to support conductors in transmission network for transmission and distribution of electricity. These towers are constructed in large numbers all over the world. The connections in electric TL classical latticed towers are peculiar compared to other types of bolted connections in buildings and bridges because (i) the angle members are connected directly or through gusset plates with bolts, (ii) the eccentric application of load due to the non-coincidence of centroid axes of angle members near the connection and (iii) members are designed as beam column element to sustain tensile or compressive forces. Bearing type bolts are used in TL towers in preference to friction type bolts, because they (i) connect thin walled angle members, (ii) are easy to use for erection at all heights, (iii) can be galvanized, (iv)erosion of galvanizing can be remedied and (v) do not require skilled personnel for installation. However, these connections are subjected to reversal of stresses due to wind load. Damage in the bolted connections generally occur due to loosening of bolts due to stress reversals (Feenstra et al. (2005) [23). The damage induced after extreme wind and earthquake may lead to collapse of the whole tower. The failure of a TL tower results in power shut down, which has huge impact on national economy. Hence, the structural safety and reliable performance of these towers are extremely important. The design of TL tower is based on minimum weight philosophy. The TL towers are highly repetitive and therefore, their designs need to be commercially competitive. The TL tower design has the following deficiencies such as misappropriate design assumptions, deficit detailing, defects in material, errors in fabrication, force fitting of members during erection, variation in grade of bolts, improper gusset plate detailing, notch cutting of member, vocalization of bolt holes, etc. Hence, to check the design and detailing aspects of members along with bolted connections and to study the behavior of tower under complex loading conditions, the prototype testing of tower is made mandatory requirement in many countries throughout the world. The structural behavior of TL tower is determined from its deflection response. Thus, the full scale testing of the towers is the only way that one can counteract the un conservatism due to structural analysis. The premature failure of TL towers occurs during prototype testing due to deficiencies in joint detailing, uncertainties in framing eccentricity, force fitting of members, unequal force distribution in bolts and gusset plate connections, etc. To have better structural response of TL tower to be tested, there is need to develop reliable model for bolted connections in TL towers. The bolted connection model plays an important role in determining the deflection response and predicting the premature member buckling failure of TL towers. The issues related to prototype testing of full scale TL towers such as fabrication errors, force fitting and notch cutting of members, application of loads, joint and crossarm detailing are discussed. The need to develop bolt slip model to simulate the actual behaviour of bolted connection in TL towers is also discussed. The bolted connections in TL towers play an important role in determining its structural behavior. The angle members used in TL towers are subjected to bi-axial bending in addition to axial load. The slip will occur in the bolted connections, due to the provision 1.5 mm bolt hole clearance. In the conventional Finite Element Analysis (FEA), the bolted connections are modeled as pin joint assuming the axial load transfer. The deflection predicted from pin joint analysis in TL towers generally does not match with experimental results. The analytical and experimental deflection value varies in the range of 30 to 50%. Hence, there is need to develop model to account bolt slip for accurate deflection and dynamic characteristic prediction of TL towers. Experimental and analytical investigations have been carried out to develop and validate bolt slip model for bolted connections in TL towers. All six degrees of freedom (both translational and rotational) have been considered to simulate the exact behaviour of bolted connections in TL towers. The model is developed based on experimental results of Ungkurapinan’s bolt slip model for axial stiffness. The rotational stiffness is formulated based on the component level experiment conducted on lap joint made of steel angle with single and double bolt subjected to tensile loading. The axial and rotational stiffness for different stages of bolt tightening is also formulated based on component level experimental investigation on lap joint. The proposed model is validated by comparing with experimental results at sub-structural level on full scale king post truss subjected to tensile loading. Further the bolt slip model is validated for different bolt tightening and failure prediction of TL tower sub panel subjected to tensile loading. Finally the proposed model is also validated for full scale TL tower for deflection prediction. NE NASTRAN, a nonlinear finite element analysis (FEA) software is used for analytical simulation and the load-deflection predictions, which are compared with the corresponding experimental results. The experimental and analytical results are in good agreement with each other. The steel pole structures are replacing the conventional lattice towers, because they have smaller plan dimension and occupy less space, when compared to lattice towers. The steel pole structures are dynamically sensitive structures and the determination of their natural frequency is extremely important. For the calculation of wind load through gust factor method, the preliminary estimation of natural frequency is required. Hence, the primary step involved in dynamic analysis is the evaluation of its natural frequency. Hence, a simplified model is proposed based on model order reduction technique for the evaluation of natural frequency of TL towers and steel pole structures. For the development of base line model to detect damage in TL towers, the natural frequency has to be updated. A semi empirical approach is proposed based on the deflection by using the proposed bolt slip model. The proposed approach of updating natural frequency is validated for different cases of member damage in TL tower sub panel, such as removal of tension, compression and hip bracing members. The transmission pole structures accumulate damage during their service life. Damage in these structures will cause a change in stiffness of the system and the physical properties of these structures, such as modal frequencies and mode shapes. Hence in the present study, the damage localization study based on modified modal strain energy approach is carried out for steel pole structures and the location of damage is identified correctly. To prevent premature failure of towers during its service life testing and failure analysis of TL towers is a mandatory requirement. In the present study, forensic failure investigation of a full scale TL tower due to deficient design of a redundant member is emphasized and the remedial measures are explained in detail. The stub failure of TL tower due to reduction in cross sectional area due to unfilled bolt hole is also discussed. To investigate the effect of unfilled bolt holes on the compression capacity of leg member, detailed FEA is carried out and compared with experimental results. The reason for failure of 9 m roof top communication tower due to redundant member deficiency is also discussed. The importance of guyed tower accessories in the guy rope design of 7 m roof top guyed pole structure is also investigated. Finally, failure investigation of compression bracing member, which has failed during testing of TL tower sub panel has been investigated. The failure load is predicted by using the proposed bolt slip model in the analysis. Thus the overall research contributions emerging from this thesis are, i) development of bolt slip model accounting for rotational stiffness, ii) development of direct method of damage detection for steel pole structures based on modified modal strain energy approach, iii) development of simplified model for prediction of natural frequency of TL tower and steel pole structures, iv) development of model updating technique through natural frequency based on semi-empirical approach and v) prediction of failure load for TL tower panel using the proposed bolt slip model.
2

Incertezas de modelo na análise de torres metálicas treliçadas de linhas de transmissão / Model uncertainties in the transmission lines latticed steel towers analysis

Kaminski Junior, Joao January 2007 (has links)
Incertezas de modelo invadem todos os estágios de uma análise de confiabilidade estrutural, desde a determinação das ações e do próprio sistema estrutural, até o processo pelo qual o efeito destas ações é avaliado. Neste trabalho, o enfoque é dado nesse último tópico, mais especificamente na avaliação das incertezas de modelo mecânico em torres metálicas treliçadas de linhas de transmissão (LT), o qual tem permanecido ignorado nas estimativas de confiabilidade até então, em parte devido a sua natureza elusiva. Logo, o problema consiste em avaliar as incertezas na predição da resposta estrutural, uma vez que todos os parâmetros que definem as ações externas e o próprio sistema são claramente definidos. A principal motivação deste trabalho partiu de um estudo conduzido pela CIGRÉ sobre torres metálicas treliçadas de LT submetidas a cargas estáticas, o qual sugere que as incertezas de modelo neste tipo de estrutura são relevantes e não podem ser desprezadas, podendo influenciar significativamente na estimativa da confiabilidade. Neste trabalho, são avaliados diferentes modelos mecânicos de torres de LT sujeitos a ações estáticas, além de modelos de torres e trechos de LT submetidos à ação dinâmica de ruptura de cabo, adotada por ser um carregamento dinâmico “bem definido”. Na análise estática, são estudados desde modelos simplificados de torres autoportantes, adotados na prática usual de projeto, até modelos mais aprimorados. A dispersão nos resultados numéricos entre os modelos é usada para quantificar as incertezas relacionadas ao modelo mecânico, e os resultados disponíveis de ensaios estáticos em protótipos são utilizados para encontrar os modelos cuja resposta mais se aproxima dos valores experimentais. A resposta dinâmica de torres metálicas treliçadas de LT submetidas à ruptura de cabo, é comparada entre vários modelos, com diferentes graus de sofisticação e detalhe. São estudados desde o modelo usual de análise e projeto de torres para este tipo de carregamento, passando por modelos relativamente simples, com uma única torre sujeita a uma carga variável no tempo, simulando o efeito da ruptura de um cabo, até modelos mais complexos de trechos de LT, os quais incluem várias torres, cabos e cadeias de isoladores. Diversas fontes de incerteza são avaliadas, considerando a influência de fatores relevantes tais como: a discretização dos elementos de cabo, as condições de contorno dos elementos de cabo das extremidades, as leis constitutivas dos elementos de barra e de cabo e o amortecimento estrutural. Por fim, são discutidas e apresentadas possíveis maneiras de considerar explicitamente a incerteza de modelo na estimativa da confiabilidade e em códigos de projeto de estruturas de linhas de transmissão. / Model uncertainties pervade all stages of a structural reliability analysis, from the description of loads and the system itself, to the process by which the effect of loads on the system is evaluated. In this study, attention is focused on the last issue, specifically in the evaluation of model uncertainties on transmission lines (TL) latticed steel towers, which has remained largely ignored in previous developments of structural reliability, in part due to its elusive nature. In essence, the problem consists of evaluating the uncertainty in response predictions, once all parameters that define the external actions and the system itself have been unequivocally prescribed. The main motivation of this thesis was a study conducted by CIGRÉ on TL latticed steel towers subjected to static loads, among other exploratory assessments, which suggests that model uncertainty is a relevant factor and cannot be disregarded, could significantly influence the outcome of reliability assessments. Herein, different mechanical models of TL self-supporting towers subjected to static loads are evaluated, besides the models of towers and TL segments submitted to dynamic load due to cable rupture, adopted by being a “well defined” loading. In the static analysis, from simplified models of self-supporting towers, like adopted in usual practice of project, to more refined models are studied. The dispersion in the numeric results among the models, together with the data of static prototype tests, are used to quantify model uncertainties. The dynamic response of latticed TL steel towers subjected to cable rupture is predicted by use of various models with different degrees of sophistication or detailing. The predictions of the various models are compared with the aim of quantifying model uncertainty. Several uncertainty sources are evaluated, considering the influence of relevant factors such as: the discretization of the cable elements, the boundary conditions of the end cable elements, the constitutive laws of cables and tower members and the structural damping. Finally, possible ways to explicitly consider model uncertainty in reliability assessments and in code formulations are discussed.
3

Incertezas de modelo na análise de torres metálicas treliçadas de linhas de transmissão / Model uncertainties in the transmission lines latticed steel towers analysis

Kaminski Junior, Joao January 2007 (has links)
Incertezas de modelo invadem todos os estágios de uma análise de confiabilidade estrutural, desde a determinação das ações e do próprio sistema estrutural, até o processo pelo qual o efeito destas ações é avaliado. Neste trabalho, o enfoque é dado nesse último tópico, mais especificamente na avaliação das incertezas de modelo mecânico em torres metálicas treliçadas de linhas de transmissão (LT), o qual tem permanecido ignorado nas estimativas de confiabilidade até então, em parte devido a sua natureza elusiva. Logo, o problema consiste em avaliar as incertezas na predição da resposta estrutural, uma vez que todos os parâmetros que definem as ações externas e o próprio sistema são claramente definidos. A principal motivação deste trabalho partiu de um estudo conduzido pela CIGRÉ sobre torres metálicas treliçadas de LT submetidas a cargas estáticas, o qual sugere que as incertezas de modelo neste tipo de estrutura são relevantes e não podem ser desprezadas, podendo influenciar significativamente na estimativa da confiabilidade. Neste trabalho, são avaliados diferentes modelos mecânicos de torres de LT sujeitos a ações estáticas, além de modelos de torres e trechos de LT submetidos à ação dinâmica de ruptura de cabo, adotada por ser um carregamento dinâmico “bem definido”. Na análise estática, são estudados desde modelos simplificados de torres autoportantes, adotados na prática usual de projeto, até modelos mais aprimorados. A dispersão nos resultados numéricos entre os modelos é usada para quantificar as incertezas relacionadas ao modelo mecânico, e os resultados disponíveis de ensaios estáticos em protótipos são utilizados para encontrar os modelos cuja resposta mais se aproxima dos valores experimentais. A resposta dinâmica de torres metálicas treliçadas de LT submetidas à ruptura de cabo, é comparada entre vários modelos, com diferentes graus de sofisticação e detalhe. São estudados desde o modelo usual de análise e projeto de torres para este tipo de carregamento, passando por modelos relativamente simples, com uma única torre sujeita a uma carga variável no tempo, simulando o efeito da ruptura de um cabo, até modelos mais complexos de trechos de LT, os quais incluem várias torres, cabos e cadeias de isoladores. Diversas fontes de incerteza são avaliadas, considerando a influência de fatores relevantes tais como: a discretização dos elementos de cabo, as condições de contorno dos elementos de cabo das extremidades, as leis constitutivas dos elementos de barra e de cabo e o amortecimento estrutural. Por fim, são discutidas e apresentadas possíveis maneiras de considerar explicitamente a incerteza de modelo na estimativa da confiabilidade e em códigos de projeto de estruturas de linhas de transmissão. / Model uncertainties pervade all stages of a structural reliability analysis, from the description of loads and the system itself, to the process by which the effect of loads on the system is evaluated. In this study, attention is focused on the last issue, specifically in the evaluation of model uncertainties on transmission lines (TL) latticed steel towers, which has remained largely ignored in previous developments of structural reliability, in part due to its elusive nature. In essence, the problem consists of evaluating the uncertainty in response predictions, once all parameters that define the external actions and the system itself have been unequivocally prescribed. The main motivation of this thesis was a study conducted by CIGRÉ on TL latticed steel towers subjected to static loads, among other exploratory assessments, which suggests that model uncertainty is a relevant factor and cannot be disregarded, could significantly influence the outcome of reliability assessments. Herein, different mechanical models of TL self-supporting towers subjected to static loads are evaluated, besides the models of towers and TL segments submitted to dynamic load due to cable rupture, adopted by being a “well defined” loading. In the static analysis, from simplified models of self-supporting towers, like adopted in usual practice of project, to more refined models are studied. The dispersion in the numeric results among the models, together with the data of static prototype tests, are used to quantify model uncertainties. The dynamic response of latticed TL steel towers subjected to cable rupture is predicted by use of various models with different degrees of sophistication or detailing. The predictions of the various models are compared with the aim of quantifying model uncertainty. Several uncertainty sources are evaluated, considering the influence of relevant factors such as: the discretization of the cable elements, the boundary conditions of the end cable elements, the constitutive laws of cables and tower members and the structural damping. Finally, possible ways to explicitly consider model uncertainty in reliability assessments and in code formulations are discussed.
4

Incertezas de modelo na análise de torres metálicas treliçadas de linhas de transmissão / Model uncertainties in the transmission lines latticed steel towers analysis

Kaminski Junior, Joao January 2007 (has links)
Incertezas de modelo invadem todos os estágios de uma análise de confiabilidade estrutural, desde a determinação das ações e do próprio sistema estrutural, até o processo pelo qual o efeito destas ações é avaliado. Neste trabalho, o enfoque é dado nesse último tópico, mais especificamente na avaliação das incertezas de modelo mecânico em torres metálicas treliçadas de linhas de transmissão (LT), o qual tem permanecido ignorado nas estimativas de confiabilidade até então, em parte devido a sua natureza elusiva. Logo, o problema consiste em avaliar as incertezas na predição da resposta estrutural, uma vez que todos os parâmetros que definem as ações externas e o próprio sistema são claramente definidos. A principal motivação deste trabalho partiu de um estudo conduzido pela CIGRÉ sobre torres metálicas treliçadas de LT submetidas a cargas estáticas, o qual sugere que as incertezas de modelo neste tipo de estrutura são relevantes e não podem ser desprezadas, podendo influenciar significativamente na estimativa da confiabilidade. Neste trabalho, são avaliados diferentes modelos mecânicos de torres de LT sujeitos a ações estáticas, além de modelos de torres e trechos de LT submetidos à ação dinâmica de ruptura de cabo, adotada por ser um carregamento dinâmico “bem definido”. Na análise estática, são estudados desde modelos simplificados de torres autoportantes, adotados na prática usual de projeto, até modelos mais aprimorados. A dispersão nos resultados numéricos entre os modelos é usada para quantificar as incertezas relacionadas ao modelo mecânico, e os resultados disponíveis de ensaios estáticos em protótipos são utilizados para encontrar os modelos cuja resposta mais se aproxima dos valores experimentais. A resposta dinâmica de torres metálicas treliçadas de LT submetidas à ruptura de cabo, é comparada entre vários modelos, com diferentes graus de sofisticação e detalhe. São estudados desde o modelo usual de análise e projeto de torres para este tipo de carregamento, passando por modelos relativamente simples, com uma única torre sujeita a uma carga variável no tempo, simulando o efeito da ruptura de um cabo, até modelos mais complexos de trechos de LT, os quais incluem várias torres, cabos e cadeias de isoladores. Diversas fontes de incerteza são avaliadas, considerando a influência de fatores relevantes tais como: a discretização dos elementos de cabo, as condições de contorno dos elementos de cabo das extremidades, as leis constitutivas dos elementos de barra e de cabo e o amortecimento estrutural. Por fim, são discutidas e apresentadas possíveis maneiras de considerar explicitamente a incerteza de modelo na estimativa da confiabilidade e em códigos de projeto de estruturas de linhas de transmissão. / Model uncertainties pervade all stages of a structural reliability analysis, from the description of loads and the system itself, to the process by which the effect of loads on the system is evaluated. In this study, attention is focused on the last issue, specifically in the evaluation of model uncertainties on transmission lines (TL) latticed steel towers, which has remained largely ignored in previous developments of structural reliability, in part due to its elusive nature. In essence, the problem consists of evaluating the uncertainty in response predictions, once all parameters that define the external actions and the system itself have been unequivocally prescribed. The main motivation of this thesis was a study conducted by CIGRÉ on TL latticed steel towers subjected to static loads, among other exploratory assessments, which suggests that model uncertainty is a relevant factor and cannot be disregarded, could significantly influence the outcome of reliability assessments. Herein, different mechanical models of TL self-supporting towers subjected to static loads are evaluated, besides the models of towers and TL segments submitted to dynamic load due to cable rupture, adopted by being a “well defined” loading. In the static analysis, from simplified models of self-supporting towers, like adopted in usual practice of project, to more refined models are studied. The dispersion in the numeric results among the models, together with the data of static prototype tests, are used to quantify model uncertainties. The dynamic response of latticed TL steel towers subjected to cable rupture is predicted by use of various models with different degrees of sophistication or detailing. The predictions of the various models are compared with the aim of quantifying model uncertainty. Several uncertainty sources are evaluated, considering the influence of relevant factors such as: the discretization of the cable elements, the boundary conditions of the end cable elements, the constitutive laws of cables and tower members and the structural damping. Finally, possible ways to explicitly consider model uncertainty in reliability assessments and in code formulations are discussed.
5

ANÁLISE DE TORRES DE LT CONSIDERANDO A INTERAÇÃO SOLO-ESTRUTURA / THE SOIL-STRUCTURE INTERACTION IN TRANSMISSION LINES LATTICED STEEL TOWERS ANALYSES

Milani, Alisson Simonetti 05 March 2012 (has links)
The mechanical model usually adopted in the design of transmission lines (TL) latticed steel towers is very simple, using spatial truss and frame elements, and solved by a linear static or non-linear geometric analysis. In the event of rupture of a conductor cable or a shield wire the loading is considered through static equivalent loads , and foundations are usually modeled how undeformable supports. This work evaluated the response of two TL latticed steel towers subjected to the cable rupture, considering the influence of foundation flexibility in the model and type of analysis, i. e., with a dynamic analysis in time domain and a static analysis with the static equivalent loads , usually adopted in design practice. In dynamic analysis, direct explicit numerical integration of the equations of motion in the time domain was adopted, using the central finite differences scheme, and the model included all components of a TL: the towers, the conductor cables, the shield wires, the insulator strings and the foundation elements, in order to evaluate the influence of boundary conditions on the results. Finally, the results of dynamic analysis of towers, in terms of displacements at the top, support reactions and maximum loads in some selected bars are compared with the results of static analysis. / O modelo mecânico usualmente adotado no projeto de torres metálicas treliçadas é bastante simples, utilizando elementos de treliça e/ou pórtico espacial, e resolvido através de uma análise estática e linear ou não linear geométrica. Nas hipóteses de carga de ruptura de um cabo condutor ou um cabo pára-raios o carregamento é considerado através de uma carga estática equivalente , e as fundações geralmente são modeladas com apoios indeslocáveis. Neste trabalho é avaliada a resposta de duas torres metálicas treliçadas de linhas de transmissão (LT) submetidas à hipótese de carga de ruptura de um cabo condutor, considerando a influência da flexibilidade da fundação no modelo e do tipo de análise, isto é, com uma análise dinâmica no domínio do tempo e uma análise estática com as cargas estáticas equivalentes usualmente adotadas na prática de projeto. Na análise dinâmica, o modelo deve contemplar todos os elementos de uma LT, ou seja, as torres, os cabos condutores, os cabos pára-raios e as cadeias de isoladores, a fim de se availar a influência das condições de contorno nos resultados. Por fim, os resultados da análise dinâmica das torres, em termos de deslocamentos no topo e esforços máximos em algumas barras, devem ser comparados com os resultados da análise estática, para que possam ser elaboradas sugestões nos procedimentos de projeto deste tipo de estrutura.
6

Análise estrutural de torres de transmissão de energia submetidas aos efeitos dinâmicos induzidos pelo vento / Structural Analysis of Transmission Line Steel Towers Subjected to Wind Induced Dynamic Effects

Marcel Isandro Ribeiro de Oliveira 13 March 2006 (has links)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Na prática corrente do projeto de torres de aço treliçadas utilizadas para suportar linhas de transmissão de energia elétrica, a avaliação do comportamento dinâmico das estruturas, de maneira geral, não é considerada. Contudo, o principal carregamento a ser considerado na análise estrutural das torres de transmissão de energia elétrica é produzido pelo vento, que atua de forma dinâmica sobre o sistema estrutural formado pelos cabos e pelas torres. Além disso, muitas estruturas desse tipo apresentam características dinâmicas desfavoráveis, o que as tornam mais vulneráveis a ação do vento.Tendo em vista que muitos acidentes envolvendo torres desse tipo ocorrem ainda que a velocidade de vento utilizada no projeto não tenha sido atingida, é possível que em muitos casos o colapso tenha sido governado pelas ações dinâmicas. Assim sendo, esse estudo tem por objetivo a utilização de uma metodologia de analise estrutural que possibilite uma avaliação mais completa acerca do comportamento das torres de transmissão de energia, considerando, obviamente, as características dinâmicas do sistema. Este trabalho de pesquisa utiliza um modelo de elementos finitos capaz de reproduzir com fidelidade o comportamento acoplado entre os cabos da linha de transmissão e estrutura quando submetidos aos carregamentos dinâmicos e não determinísticos produzidos pelo vento. O modelo tridimensional estudado é constituído por elementos finitos de pórtico e treliça espacial e considera o efeito de não-linearidade geométrica decorrente, principalmente, dos grandes deslocamentos sofridos pelos cabos e isoladores. O carregamento do vento é modelado como um processo aleatório a partir das suas propriedades estatísticas. Os resultados obtidos ao longo desse estudo mostram que a parcela dinâmica da resposta das estruturas pode ser determinante no seu comportamento. Nesse caso, a utilização de uma análise estrutural estática pode resultar no mau dimensionamento das torres e, conseqüentemente, em possíveis acidentes. / In the current design process of steel latticed towers used to support electrical transmission lines, the structures dynamic behaviour is not considered. However, the main loading to be taken into account in the electrical transmission line towers structural analysis is produced by the wind, which acts dynamically over the structural system composed by towers and cables. In addition, its not uncommon for slender towers to present disadvantageous dynamic properties, making them vulnerable to the wind action. Considering that many accidents associated to this kind of structure occur even for wind velocities below that specified in the design process, its possible that most of these accidents have been produced by dynamic actions. Therefore, this study aims to develop a structural analysis method that allows for a more accurate evaluation of the electrical transmission towers behaviour, considering its intrinsic dynamic effects. This study proposed the use of a finite element model that can accurately simulate the coupled behaviour between the transmission line cables and the suspension structures when subjected to the dynamic random loading produced by the wind. The proposed three-dimensional model is composed by beam and truss spatial finite elements and accounts for the geometric non-linearity effects produced by the large displacements associated to the line cables and insulators. The wind loading is modelled as a random process based on its statistical properties. Results obtained throughout this study have indicated that the dynamic response can be very meaningful for the system structural behaviour. In this case, the use of a static structural analysis can lead to a non-trustable design of the towers and, consequently, to potential structural failures.
7

Análise estrutural de torres de transmissão de energia submetidas aos efeitos dinâmicos induzidos pelo vento / Structural Analysis of Transmission Line Steel Towers Subjected to Wind Induced Dynamic Effects

Marcel Isandro Ribeiro de Oliveira 13 March 2006 (has links)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Na prática corrente do projeto de torres de aço treliçadas utilizadas para suportar linhas de transmissão de energia elétrica, a avaliação do comportamento dinâmico das estruturas, de maneira geral, não é considerada. Contudo, o principal carregamento a ser considerado na análise estrutural das torres de transmissão de energia elétrica é produzido pelo vento, que atua de forma dinâmica sobre o sistema estrutural formado pelos cabos e pelas torres. Além disso, muitas estruturas desse tipo apresentam características dinâmicas desfavoráveis, o que as tornam mais vulneráveis a ação do vento.Tendo em vista que muitos acidentes envolvendo torres desse tipo ocorrem ainda que a velocidade de vento utilizada no projeto não tenha sido atingida, é possível que em muitos casos o colapso tenha sido governado pelas ações dinâmicas. Assim sendo, esse estudo tem por objetivo a utilização de uma metodologia de analise estrutural que possibilite uma avaliação mais completa acerca do comportamento das torres de transmissão de energia, considerando, obviamente, as características dinâmicas do sistema. Este trabalho de pesquisa utiliza um modelo de elementos finitos capaz de reproduzir com fidelidade o comportamento acoplado entre os cabos da linha de transmissão e estrutura quando submetidos aos carregamentos dinâmicos e não determinísticos produzidos pelo vento. O modelo tridimensional estudado é constituído por elementos finitos de pórtico e treliça espacial e considera o efeito de não-linearidade geométrica decorrente, principalmente, dos grandes deslocamentos sofridos pelos cabos e isoladores. O carregamento do vento é modelado como um processo aleatório a partir das suas propriedades estatísticas. Os resultados obtidos ao longo desse estudo mostram que a parcela dinâmica da resposta das estruturas pode ser determinante no seu comportamento. Nesse caso, a utilização de uma análise estrutural estática pode resultar no mau dimensionamento das torres e, conseqüentemente, em possíveis acidentes. / In the current design process of steel latticed towers used to support electrical transmission lines, the structures dynamic behaviour is not considered. However, the main loading to be taken into account in the electrical transmission line towers structural analysis is produced by the wind, which acts dynamically over the structural system composed by towers and cables. In addition, its not uncommon for slender towers to present disadvantageous dynamic properties, making them vulnerable to the wind action. Considering that many accidents associated to this kind of structure occur even for wind velocities below that specified in the design process, its possible that most of these accidents have been produced by dynamic actions. Therefore, this study aims to develop a structural analysis method that allows for a more accurate evaluation of the electrical transmission towers behaviour, considering its intrinsic dynamic effects. This study proposed the use of a finite element model that can accurately simulate the coupled behaviour between the transmission line cables and the suspension structures when subjected to the dynamic random loading produced by the wind. The proposed three-dimensional model is composed by beam and truss spatial finite elements and accounts for the geometric non-linearity effects produced by the large displacements associated to the line cables and insulators. The wind loading is modelled as a random process based on its statistical properties. Results obtained throughout this study have indicated that the dynamic response can be very meaningful for the system structural behaviour. In this case, the use of a static structural analysis can lead to a non-trustable design of the towers and, consequently, to potential structural failures.

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